The research described involves two major projects. The central aims of these two projects are to elucidate: 1. The cell-specific mechanisms that direct expression of the growth hormone (GH) and prolactin (PRL) genes to different cell types. 2. The signal transduction pathways employed by peptide hormones to regulate pituitary expression of the PRL gene. These studies will be performed with the GH3 rat pituitary cells and other cell lines. One of the aims of Project 1 is to further investigate cell- specific repression of the GH gene. To do this we will investigate whether transcription in vitro of chromatinized templates can be employed to study GH promoter repression; further investigate a recently characterized GH promoter repressor sequence and its DNA-binding proteins; and pursue the use of F9 embryonal carcinoma cells as a model for early embryogenic repression of the PRL and GH genes. Two other aims of Project 1 are to characterize further the regulatory properties of multiple sites in the promoters of these genes that bind the transcription factor pit-1; and to employ a genetic technique, recently developed with L. Chasin (Columbia University), to attempt to clone genes involved, directly or indirectly, in developmental regulation of the PRL gene. The immediate aim of Project 2 is based on our recent finding that the proximal pit-1 binding site in the PRL promoter is also a response element for thyrotropin-releasing hormone (TRH). We are now investigating how pit-1 mediates the action of this peptide hormone, and whether TRH can also regulate the PRL promoter independently of pit-1. In similar studies, directed to understanding the complex hormonal regulation of the PRL gene, the actions of the phorbol ester TPA, and of two other peptide hormones (epidermal growth factor and vasoactive intestinal peptide) on the PRL promoter will be further investigated.